Hypertension
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We studied the total vascular pressure-volume relationship and cardiac output (CO) in conscious rats receiving DOCA-salt or sham treatment. The mean circulatory filling pressure (MCFP) was measured by briefly inflation an indwelling balloon in the right atrium, and the MCFP-blood volume (BV) relationship over +/- 10% of BV was determined by rapid blood infusion or withdrawal. CO was measured in separate experiments using Fick's principle. ⋯ Arterial compliance decreased at 5 and 8 weeks. CO remained unaltered at 1, 2, 5, and 8 weeks. These results suggest that the altered total vascular capacity may serve to maintain a normal CO against a rising afterload in the conscious DOCA-salt hypertensive rats, and that the decreased total vascular capacity may be a secondary hemodynamic feature with progression of hypertension.
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Whole-body venous capacity was examined in conscious 4-month-old male spontaneously hypertensive rats (SHR) and Wistar-Kyoto normotensive (WKY) rats by determining mean circulatory filling pressure (MCFP) and blood volume. The MCFP was determined in conscious animals after briefly arresting the circulation by inflating an indwelling balloon in the right atrium. Blood volume was determined by dilution of 125I-albumin and 51Cr-red cells. ⋯ The linear regression line for delta interstitial fluid pressure and delta fluid volume was estimated for each rat and the inverse of this slope represented ETTC, which averaged 7.4 +/- 1.0 and 9.6 +/- 2.1 ml/kg/mm Hg (p greater than 0.3) in SHR and WKY respectively. Thus, there were no significant differences in interstitial fluid pressure or ETTC between female SHR and WKY. The results of this study confirm a decreased venous capacity in male SHR with established hypertension and provide new information indicating no measurable abnormalities in interstitial fluid pressure or effective total tissue compliance in adult female SHR as compared with WKY.